1. Field of the Invention
The present invention relates to a characteristic measuring apparatus for electronic components, and more particularly, to an improvement to a structure of a holder for holding electronic components to be tested for the electrical characteristic.
2. Description of the Related Art
U.S. Pat. No. 5,842,579 discloses a known electronic-component characteristic measuring apparatus that is relevant to the present invention. FIG. 9 schematically shows the principal part of the known electronic-component characteristic measuring apparatus.
Referring to FIG. 9, a characteristic measuring apparatus 1 is used to measure the characteristic of a chip-shaped electronic component 4 having first and second external terminal electrodes 2 and 3 at first and second opposing ends thereof.
The characteristic measuring apparatus 1 includes a holder 8 that has a receiving cavity 5 for receiving an electronic component 4 and that holds the electronic component 4 with the first and second external terminal electrodes 2 and 3 pointing toward first and second opposing open ends 6 and 7 of the receiving cavity 5.
The characteristic measuring apparatus 1 also includes first and second measuring terminals 9 and 10 disposed at the first and second open ends 6 and 7 of the receiving cavity 5 so as to be in contact with the first and second external terminal electrodes 2 and 3 of the electronic component 4. The first measuring terminal 9 is made of, for example, a leaf spring to be in elastic contact with the first external terminal electrode 2. The second measuring terminal 10 is shaped like, for example, a block, and is fixedly provided.
The holder 8 is normally shaped like a disk, and a plurality of receiving cavities 5 are distributed in the circumferential direction therein. Each of the receiving cavities 5 receives one electronic component 4. Therefore, it should be understood that only a portion of the holder 8 is shown in FIG. 9.
The disc-shaped holder 8 is rotated. An electronic component 4 is put into a receiving cavity 5 at a predetermined position on a path along which the receiving cavity 5 is moved by the rotation of the holder 8. Subsequently, the electronic component 4 held in the receiving cavity 5 is moved between the first and second measuring terminals 9 and 10, and the first and second measuring terminals 9 and 10 come into contact with the first and second external terminal electrodes 2 and 3 to measure the electrical characteristic of the electronic component 4. After that, the electronic component 4 is ejected from the receiving cavity 5. In this case, electronic components 4 are sorted according to the measured electrical characteristic, for example, depending on whether the electrical characteristic is good.
When the electrostatic capacitance of the electronic component 4 is determined using the above-described characteristic measuring apparatus 1, in actuality, it is determined using the following procedure in order to increase the accuracy.
First, an electrical parasitic component given by electrical elements, such as the measuring terminals 9 and 10 and cables (not shown), provided in the characteristic measuring apparatus 1 is measured beforehand. Subsequently, the electrostatic capacitance of the electronic component 4 is measured. The measured electrostatic capacitance is a value including the electrical parasitic component. The value obtained by subtracting the electrical parasitic component from the measured electrostatic capacitance of the electronic component 4 is regarded as the electrostatic capacitance of the electronic component 4.
Therefore, when there is a difference between the electrical parasitic component measured beforehand and the electrical parasitic component obtained when the electronic component 4 is actually tested, the difference is included as an error in the measured electrostatic capacitance.
The above-described electrical parasitic component includes a stray capacitance between the measuring terminals 9 and 10. In FIG. 9, electric lines of force 11 that produce the stray capacitance are schematically shown by broken arrows. As the size of the electronic component 4 decreases and the distance between the first and second measuring terminals 9 and 10 thereby decreases, and as the opposing area between the first and second measuring terminals 9 and 10, the stray capacitance becomes less negligible.
When there are variations in the size of the electronic components 4 under such a condition, the stray capacitance varies because of the size variations. As a result, a difference is formed between the electrical parasitic component obtained when characteristic is measured and the electrical parasitic component measured beforehand, and the difference changes. An error produced thereby is included in the measured electrostatic capacitance.
A similar problem is also encountered not only when the electrostatic capacitance is measured, but also when other electrical characteristics are measured.